This application claims the priority of Japanese Patent Application No. 9-180395 filed on Jun. 19, 1997.
1. Field of the Invention
The present invention relates to a lithium secondary battery and, more particularly, to an improvement of an electrolytic salt of a nonaqueous electrolyte for the purpose of improving a storage characteristic of the secondary battery of this type in a charged condition (hereinafter referred to as "charge-storage characteristic").
2. Description of the Prior Art
Battery characteristics of the lithium secondary battery depend largely on the kind of nonaqueous electrolyte employed. Therefore, several kinds of nonaqueous electrolytes comprising electrolytic salts (solutes) and solvents have been heretofore proposed. For example, it is disclosed in the Japanese Laid-Open Patent Publication (unexamined) No. 8-31452 that a charge-discharge cycle life is improved by employing as an electrolytic salt LiN(CF.sub.3 SO.sub.2).sub.2 (lithiumtrifluoromethanesulfonyl imide) which is highly stable with respect to the solvent and difficult to be decomposed at the time of charge-discharge reaction.
However, as a result of researches conducted by the inventors, it has been found that in the lithium secondary battery in which LiN(CF.sub.3 SO.sub.2).sub.2 alone is employed as the electrolytic salt, there is a problem of considerable self-discharge when the battery is stored in a charged state.